1. Field of the Invention
The invention relates to a bearing apparatus and a method for feeding lubricant to a bearing, and in particular, to a bearing apparatus equipped with a mechanism configured to feed lubricant to a bearing and a method for feeding lubricant in the apparatus.
2. Description of the Related Art
Japanese Patent Application Publication No. 2013-60999 (JP 2013-60999 A) and Japanese Patent Application Publication No. 2013-83335 (JP 2013-83335 A) propose bearing apparatuses in which a bearing is equipped integrally with a unit configured to feed lubricant to the bearing. In such a bearing apparatus, lubricant is stored in the unit so that a specified amount of lubricant is fed to the bearing at a specified timing, for example, by a pump included in the unit.
The bearing apparatus equipped with the unit configured to feed lubricant to the bearing needs supply of lubricant stored in the unit. Thus, for enhanced maintainability of the bearing apparatus, keeping the frequency of supply of lubricant to the unit low is effective. An example of measures for keeping the frequency of supply of lubricant low is to set the amount of lubricant discharged from the unit and fed to the bearing to an ultratrace flow rate lower than a picoliter-scale flow rate.
The viscosity of oil is affected by temperature, and thus, a unit ambient temperature may affect the velocity of discharge of lubricant from the unit and the amount of lubricant discharged. Specifically, when the lubricant temperature is low, the viscosity tends to increase, leading to a reduced discharge velocity of the lubricant. As a result, the lubricant may fail to be fed to a designed position inside the bearing. When the lubricant temperature is low, the amount of lubricant discharged tends to be reduced. This may prevent a designed amount of lubricant from being fed to the bearing. In particular, a decrease in the amount of lubricant discharged from the unit makes the adverse effect of the ambient temperature more serious.